A constitution whose authority derives from popular sovereignty may be sustained, altered, or abandoned by, and only by, the sovereign people. Judicial supremacy - the theory that constitutional politics must be pursued through judicial review by a constitutional court - should be discarded, in favor of the exercise of constituent power through "contestatory constitutionalism:" a complex of participatory democracy, popular engagement with existing institutions, and the articulation of constitutional claims in the modality of politics rather than law. The dissertation argues for the priority of contestatory constitutionalism over judicial supremacy and competing theories of judicial interpretation of the constitutional text, by presenting an account of American constitutional development and its associated pathologies, assessing and refining the idea of popular constitutionalism (that is, popular interpretation of the Constitution), and defending contestatory constitutionalism, considered as the most preferable interpretation of popular constitutionalism, against judicial supremacy. Contestatory constitutionalism should also be preferred over competing theories that argue for more limited forms of judicial interpretive authority, such as originalism, which holds that particular interpretations of political and legal history should trump contemporary understandings and preferences; and living constitutionalism, which holds that constitutional meaning should be under constant revision across political time. Contestatory constitutionalism elides the debate between originalists and living constitutionalists; it focuses on the distribution and disposition of power, participation, and persuasion within the polity itself, and not on the fixation or fluidity of meaning in the constitutional text.